This invention is particularly useful in machine tools for exchange of parts or tools between positions which are located on intersecting coordinate axes, the part being in alignment or one of the axes in each position. In a tool exchanging machine, for example, such an exchange might be between a spindle extending horizontally out from the front of the machine to a storage position either on top of the machine or on the side of the machine; in either case requiring an arcuate movement of the exchanged parts through 90.degree.. In the prior art when such a movement was required and made by a rotating arm mechanism with a gripper at each end, a symmetrical exchange was made. Each of the two positions between which movement of the tools was made was located along its respective coordinate axis such that each position was equidistant from the intersection of the axes (origin). A typical mechanism for an exchange of this type is shown in U.S. Pat. No. 3,722,711 issued to W. B. Seidel. In this type mechanism a central mechanism supports arms on either side and by rotation of the central mechanism the positions in space of the arms are reversed alternately in exchange movements. The central mechanism rotates on an axis which extends from the origin of the coordinate axes and which bisects the angle between the coordinate axes. The axes of the spindle and storage position may be separated by an angle other than 90.degree. but the axis on which the central mechanism rotates will nevertheless bisect this angle.
In some applications, it is desirable to locate positions between which exchange of parts is to be made at positions that are not equidistant from the origin of the axes through these positions. This might be done, for example, to reduce the overhang of a member which is subject to large forces when in use. Such a structure might be a machine tool spindle subjected to high forces in a machining operation. The tool or part storage apparatus might be placed at a substantial lateral or vertical distance from the spindle so that it does not interfere with spindle use.
It is therefore an object of this invention to provide an asymmetrical article exchange mechanism. The mechanism is useful in the simultaneous exchange of parts between two positions located on intersecting axes but which positions are not located equidistant from the origin of the axes.